(a) Field of the Invention
The present invention describes a method for restoring the thickness of a damaged or degenerated fat-pad.
(b) Description of Prior Art
Heel pain is a common complaint that leads, every year, about 1% of the North-American population to consult a physician. The pain is most often due to plantar fasciitis or to heel spurs. Those conditions can usually be traced to accidents or specific activities, but are often aggravated by an atrophy of the calcaneal fatty pad. This fat-pad cushion plays a critical biomechanical role in absorbing the impact of walking and running by distributing the load and absorbing energy upon impact.
The fat-pads are cushions made of communicating pockets of fascia filled with fatty acids. Anatomically, three distinct fatty pads can be clearly identified below the plantar surface, at the three contact points with the ground, i.e. under the heel, on the metatarsal head, and on the outer arch contact area.
Blechschmidt (Blechschmidt, E., Die Architektur des Fersenpolsters. Gegenbaurs Morphologisches Jarhbuch, 73: 20-68, 1934 (translated and re-edited as: Blechschmidt, E., The Structure of the Calcaneal Padding. Foot & Ankle, 2: 260-283, 1982) performed a thorough study, using sagittal, frontal as well as horizontal sections to map the anatomical structure of those pads throughout the development of foetus and adults. This work documented well the structure of the pads, and brought the first clues on how this would relate to their physiological role. The pads are composed of septa forming a trabecular network of intercommunicating chambers. Those chambers are disposed in whorls, which follow the curvature and torsion of the calcaneus itself. This arrangement suggested some form of biomechanical optimisation.
Most attempts to study the biomechanics of the heel pad were based on the load-deformation curves obtained from in vivo impact experiments, through pendulum and drop tests, or by using force platform. Others performed in vitro experiments (Bennett, M. B. and Ker, R. F., Journal of Anatomy, 171: 131-138, 1990; and Aerts, P., et al., Journal of Biomechanics, 28: 1299-1308, 1995; and Ker, R. F., Journal of Experimental Biology, 199(Pt 7):1501-1508, 1996). All results highlighted the efficiency of the pads to cushion the musculoskeletal system from ground-heel impacts, and brought some insight into the comprehension of the pads' physiological role in the biomechanics of the foot. It then appeared that the heel fat pad has a structure optimised for load bearing (Jahss, M. H., et al., Foot & Ankle, 13: 227-232, 1992).
Further information came from studying the fatty acid composition of the heel fat pad (Buschmann, W. R., et al., Foot & Ankle, 14: 389-394, 1993). Using capillary gas-liquid chromatography, this group determined that the fat pads of normal individuals is mainly composed of the following mixture of fatty acids:
TABLE 1Fatty acid composition of the heel fat padFatty acidfractionS.D.Myristate 1.6%0.5%Palmitate13.6%2.2%Stearate 1.5%0.8%Palmitoleate10.6%1.9%Vaccenate 4.1%1.1%Oleate40.6%2.4%Linoleate14.6%2.8%Sum:86.6%
The physiological mechanics of the pads relies on the motion of fatty acids constrained within a complex septal system. This system is analogous to a mechanical dashpot. Its characteristics depend on the porosity of the trabecular network, studied by Blechschmidt (Blechschmidt, E., Die Architektur des Fersenpolsters. Gegenbaurs Morphologisches Jarhbuch, 73: 20-68, 1934 (translated and re-edited as: Blechschmidt,E., The Structure of the Calcaneal Padding. Foot & Ankle, 2: 260-283, 1982)), and on the properties of the fatty acids (Buschmann, W. R., et al., Foot & Ankle, 14: 389-394, 1993). The ratio of unsaturated fatty acids to saturated fatty acids indeed affects the properties of the fat, and modifies the biomechanical properties of the pads (Jahss, M. H., et al., Foot & Ankle, 13: 227-232, 1992).
The fat pads normally become atrophic with age (D'Ambrosia, R. D., Orthopedics, 10:137-142, 1987; and Jahss, M. H., et al., Foot & Ankle, 13: 227-232, 1992), but the risk of premature atrophy increases if the individual is overweight, has diabetes (Alexander, R. McN., et al., Journal of Zoology—London, A209: 405-419, 1986), has often worn thin-sole or high-heel shoes. Also, the treatment of plantar fasciitis with cortisone injections leads to further atrophy of the pads (D'Ambrosia, R. D., Orthopedics, 10:137-142, 1987). Atrophic cushions usually have reduced height due to a loss of fatty acid substance, or from herniation of the fascia (Buschmann, W. R., et al., Foot & Ankle, 16: 254-258, 1995). Thin fat pads can be very uncomfortable, and can lead to painful pathologies (Narváez, J. A., et al., Radiographics, 20: 333-352, 2000). A comparative experiment on 200 heel pads demonstrated that the feet with thinnest fat pads also had the lowest shock absorbency.
Plantar injections of silicone fluid have been used to relief localised pressure-related foot disorders, such as corns and calluses (Balkin, S. W., Fluid silicone implantation of the foot. In Neale's common foot disorders: diagnosis and management. 5th ed. Lorimier, D., Churchill Livingstone, U.K., 387-400, 1997) and to reduce risk factors for ulceration in diabetic foot (Van Schie, C. H. M., et al., Diabetes Care, 23: 634-638, 2000). Silicone is engulfed and retained within histocyte cell body as microscopic droplets, and stimulates the local deposition of collagen fibres. It thickens the skin at the site of injection, by inducing the local formation of scar-like fibrous tissue. It is not compatible with the normal fatty acid composition, and does not participate in restoring the normal physiological function of the fat pad.
The ageing and active segments of the population are especially affected by fat pad atrophy. With the normal loss of fat pads, pressure area starts developing over the metatarsal and the heel area as early as age 30 (D'Ambrosia, R. D., Orthopedics, 10:137-142, 1987). The individuals suffering from this condition currently rely only on orthoses and in-sole cushioning. It would thus be highly desirable to develop a method for restoring the thickness of the pads, and consequently their cushioning function.